[Guest]

It´s obviously a move targeted at mirrorless competitors to defend or expand market share and an interesting addition to the entry level interchangeable lens cameras mass market.

 

That's what I think too.   Canon does seem to have a problem on the sensory front. We keep seeing the recycled 18MP sensor now for a long time, and the 7D II takes its time, because I think they want to get the next generation sensor in there, which they haven't really managed to release yet. And as obvious with the EOS-M, they have not managed to really solved well the AF in a mirror-less situation, even though they put the phase-dots on the sensor. In a way the 100D is an admission by Canon that they can't make a good AF on sensor yet, and they compete by shrinking the mirror-box body.

 

Now, if you think about it, those mirror-less cameras that do have a viewfinder, they are not that much smaller than the 100D, except for the depth due to the mount. So, for the higher end mirror-less market, a 100D with fast phase AF due to the mirror, should be a very compelling competition.  

As for smaller lenses, only lenses in the approximately the 20 to 40mm focal range would benefit from the mirror-less design, due to reduced flange distance, so you don't need retrofocus  lens designs. That's why you have e.g. the EOS-M 22mm pancake, but the EF/EF-S pancake is 40mm. The larger lenses still would stay essentially the same since the sensor is the same for APS-C, where focal length and aperture dictate size of the lens.  m4/3  and 4/3 would have a bit of an advantage because of smaller lenses,  due to a little smaller image circle, and shorter focal lengths that give you a bit extended reach (the "crop" factor advantage).  But the extended reach works only if m4/3 has a higher pixel density.   If Canon would manage to come up with a 24Mp sensor  that is similar quality as the 16MP in the Olympus OMD EM-5 (and Sony/Nikon have those already), then there is no advantage for 4/3 anymore either, since you just crop the image. The only advantage remaining is the smaller image circle, which disappears for tele lenses.  And the pixel density on sensors can't be made smaller forever, due to diffraction, it's effect can already be seen here in the lens tests.